Simple Interest Calculator

What the Simple Interest Calculator does

This tool works out how much interest a fixed sum earns or costs over time using the classic simple interest formula. Unlike compound interest, simple interest is calculated only on the original amount you start with, so it grows at a steady, predictable rate every year. It is useful for anyone comparing a short term loan, a fixed deposit, a personal IOU, or a savings plan, and for students learning the formula behind it.

For every calculation you get two clear figures: the total interest over the whole period, and the final balance, which is your starting amount plus that interest. That makes it easy to see the full cost or return at a glance.

How to use it

1. Enter the starting amount in the Principal field.
2. Set the yearly rate in the Annual rate (%) field, for example 5 for five percent.
3. Type how long the money is held in the Years field.
4. Click Calculate to see the total interest and the final balance.
5. Adjust any field to compare different rates, terms, or amounts straight away.

A worked example

Say you put 1000 into the Principal field, set the Annual rate (%) to 5, and enter 10 in the Years field. The calculator multiplies 1000 by 0.05 by 10 and returns 500 in total interest, giving a final balance of 1500. Because the interest never compounds, the yearly amount (50 here) stays the same for the entire term, which keeps the result simple to verify by hand.

Everything runs right in your browser, so your numbers stay private on your own device. It is completely free, works instantly, and needs no sign-up.